Image taking apparatus and lens apparatus

ABSTRACT

An image taking apparatus performs a focusing operation quickly and includes a light splitting unit which splits a light flux from an image-taking lens into a plurality of light fluxes, a view finder optical system observing an object image formed by the light flux from the lens, an image pickup element which photoelectrically converts the object image to an electrical signal and a focus detector detecting the focusing state of the lens according to a phase difference detector. Here, the light splitting unit changes between a first state for directing the light flux to the view finder optical system and the focus detector, a second state for directing the light flux to the image pickup element and the focus detector, and a third state in which the light flux is directed only to the image pickup element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image taking apparatus having thefunction of focusing an objective lens and the function of observing anobject image formed by the objective lens and a lens apparatus mountedon the image taking apparatus.

2. Description of the Related Art

When an object is observed through an optical view finder (OVF) of asingle-lens reflex camera, which is one of optical apparatuses, a lightflux emitted from the objective lens is reflected by a reflecting mirrorprovided on an optical path behind the objective lens (image plane side)to change its optical path and introduced into an optical view finderincluding a pentaprism, etc. This makes it possible to see an objectimage formed by the light flux which has passed through the objectivelens as a normal image. At this time, the reflecting mirror is placeddiagonally on the image-taking optical path.

On the other hand, when the objective lens is used as an image-takinglens (when an image is taken), the reflecting mirror is instantaneouslywithdrawn from the image-taking optical path and an image-taking lightflux which has passed through the objective lens is formed on an imagepickup medium (film and an image pickup element such as CCD). Then, whenthe image-taking operation is completed, the reflecting mirror isinstantaneously placed diagonally on the image-taking optical path.

In a digital camera, in response to a release button depressingoperation, an object image is exposed to light for a desired time on animage pickup element such as a CCD or CMOS sensor and an image signalexpressing one still image obtained through photoelectrical conversionof the image pickup element is converted to a digital signal. Then, byapplying predetermined processing such as YC processing to the converteddigital signal, an image signal of a predetermined format is obtained.

The digital image signal expressing the picked up image is recorded in asemiconductor memory for each image. The recorded image signal is readout from the memory and displayed on a display unit of the camera,reproduced as a printable signal or output to and displayed on a displaydevice, etc.

One type of the above described camera is a single-lens reflex typedigital camera which allows manual selection of a focusing operationaccording to a phase difference detection system or focusing operationaccording to a contrast detection system as disclosed, for example, inJapanese Patent Application Laid-Open No. 2001-275033 (hereinafterreferred to as “Document 1”).

Furthermore, in a single-lens reflex type digital camera provided withan optical view finder and electric view finder (EVF) as disclosed, forexample, in Japanese Patent Application Laid-Open No. 2001-125173(hereinafter referred to as “Document 2”), when the reflecting mirror isplaced diagonally on the image-taking optical path, focus detectionaccording to a phase difference detection system is performed based onthe light flux reflected by the reflecting mirror and when thereflecting mirror is withdrawn from the image-taking optical path, focusdetection according to a contrast detection system is performed usingthe output of an image pickup element which receives the image-takinglight flux.

In the camera disclosed in above Document 2, it is possible toelectronically display the image which has been taken while performingfocusing based on the output of the image pickup element even when thereflecting mirror is in a position withdrawn from the image-takingoptical path. Therefore, the photographer can take images while checkingthe focusing state of the image which is electronically displayed on,for example, an organic EL display.

On the other hand, in focusing control, to increase the speed ofdeciding the focusing direction (driving direction of image-takinglens), there is a focusing apparatus provided with a step in a lightdetecting surface of the image pickup element as disclosed, for example,in Japanese Patent Application Laid-Open No. 2001-215406 (hereinafterreferred to as “Document 3). That is, the optical path length isdifferentiated by a micro distance, a plurality of image signals arecollected and the focusing direction is decided based on the collectedimage signal. Then, the image-taking lens is moved to the in-focusposition in the decided focusing direction.

Furthermore, as disclosed, for example, in Japanese Patent ApplicationLaid-Open No. 2000-162494 (hereinafter referred to as “Document 4),there is a camera system provided with a focus detection unit accordingto a phase difference detection system in each of a lens apparatus and acamera body. The method of detecting a focusing state according to aphase difference detection system is disclosed, for example, in PatentPublication No. H5(1993)-88445 (hereinafter referred to as “Document5”).

The camera disclosed in above described Documents 1 and 2 performsfocusing according to the contrast detection system, but this detectionsystem has a problem that it takes time to reach an in-focus state.

The focusing according to the contrast detection system calculates thesharpness of an object image formed by the image-taking optical systemthrough an evaluation using a predetermined function based on the outputof the image pickup element and adjusts the position on the optical axisof the image-taking optical system in such a way that the function valuetakes an extreme value. There are various evaluation functions such asadding up absolute values of differences in brightness signals ofadjacent pixels within the focus detection area, and adding up thesquares of differences in brightness signals of adjacent pixels withinthe focus detection area or likewise processing differences in signalsof adjacent pixels of R, G and B image signals.

The focusing according to the contrast detection system calculates anevaluation function value while slightly changing the position on theoptical axis of the image pickup optical system (focusing lens), andthereby takes a considerable time until an in-focus state is achieved.

On the other hand, in the focusing apparatus disclosed in the abovedescribed Document 3, the speed of the focusing operation is enhanced,but pixels of a short optical path length and pixels of a long opticalpath length are mixed, which makes it not possible to obtain a highquality image. Here, shortening the difference in the optical pathlength between pixels of a short optical path length and pixels of along optical path length makes it possible to improve the image qualitybut it is difficult to decide the focusing direction in focusingcontrol. Therefore, the above described focusing apparatus cannotrealize high-speed focusing control and improvement of image qualitysimultaneously.

The camera system disclosed in above described Document 4 is providedwith a focus detection unit according to a phase difference detectionsystem, and can thereby recognize a defocus amount through a singlefocus detection operation. For this reason, if a focusing lens of theobjective lens unit is driven based on the defocus amount, one-time lensdriving is all that is required to reach an in-focus state allowingextremely high speed focusing.

Furthermore, in the above described camera system, the reflecting mirroris kept withdrawn from the image-taking optical path during continuousimage-taking, the focal plane shutter is fully open and the focusdetection unit in the lens apparatus performs a focus detectionoperation. Therefore, even if the reflecting mirror is withdrawn and thefocus detection unit in the camera body is not operating, it is possibleto perform high-speed focusing based on the focus detection by the focusdetection unit in the lens apparatus.

However, since the above described camera system is provided with twofocus detection units, the system becomes a large and costly system.

SUMMARY OF THE INVENTION

One aspect of the image taking apparatus of the present inventioncomprises a light splitting unit which splits a light flux from animage-taking lens into a plurality of light fluxes, a view finderoptical system for observing an object image formed by the light fluxfrom the image-taking lens, an image pickup element whichphotoelectrically converts the object image to an electrical signal anda focus detection unit for detecting the focusing state of theimage-taking lens according to the phase difference detection system.Here, the light splitting unit changes between a first state in whichthe light flux is directed to the view finder optical system and thefocus detection unit and a second state in which the light flux isdirected to the image pickup element and the focus detection unit.

Another aspect of the image taking apparatus of the present inventioncomprises an image pickup element which photoelectrically converts anobject image to an electrical signal, an image display unit whichdisplays image data acquired using the image pickup element, a controlcircuit which controls the driving of the image display unit and amirror member which can move with respect to the image-taking opticalpath and allows at least part of the image-taking light flux to pass tothe image pickup element side when the mirror member is inserted in theimage-taking optical path. Here, the control circuit causes the imagedisplay unit to display only part of the image data when the mirrormember is inserted the image-taking optical path.

One aspect of the lens apparatus of the present invention comprises alens apparatus mounted on an image taking apparatus having a first modein which a light flux from the object is directed to a view finderoptical system and a focus detection unit and a second mode in which thelight flux is directed to an image pickup element and the focusdetection unit comprising; a communication unit which communicates withthe image taking apparatus; a light quantity adjusting unit whichcontrol the quantity of the light flux directed to the image takingapparatus; and a control circuit which controls the driving of the lightquantity adjusting unit according to the communication of thecommunication unit. Here, the control circuit changes the practice ofthe control of the light quantity adjusting unit according to the firstmode and the second mode.

The features of the image taking apparatus of the invention will becomemore apparent from the following detailed description of preferredembodiments with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a camera system which isEmbodiment 1 of the present invention;

FIG. 2 is a longitudinal sectional view of the camera system;

FIG. 3 is a longitudinal sectional view of the camera system;

FIG. 4 is a longitudinal sectional view of the camera system;

FIG. 5 is a longitudinal sectional view of the camera system;

FIG. 6 is a schematic structure of the camera system;

FIG. 7 is a block diagram showing an electrical structure of the camerasystem;

FIG. 8 is a flow chart illustrating an image-taking sequence of thecamera system;

FIG. 9 is flow chart illustrating a view finder mode switchingoperation;

FIG. 10 illustrates waveforms of output signals of a focus detectionsensor;

FIG. 11 illustrates waveforms of the output signals of the focusdetection sensor;

FIG. 12 illustrates a relationship between a field of view that can beoutput to an electronic image display in real time and a field of viewof the picked up image;

FIG. 13 illustrates a relationship between a field of view that can beoutput to the electronic image display in real time and a field of viewof the picked up image; and

FIG. 14 illustrates operations of an optical path splitting systemaccording to Embodiment 2 (A to E).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

With reference now to FIG. 1 to FIG. 7, a camera system which isEmbodiment 1 of the present invention will be explained.

FIG. 6 is a side cross-sectional view showing a schematic structure ofthe camera system which is this embodiment. The camera system of thisembodiment is a single-panel digital color camera using an image pickupelement such as a CCD or CMOS sensor and obtains an image signalexpressing a moving image or still image by driving the image pickupelement continuously or sporadically. Here, the image pickup element isa type of area sensor which converts received light to an electricsignal for each pixel, stores charge according to the light quantity andreads out this stored charge.

In FIG. 6, reference numeral 101 denotes a camera body and members whichwill be explained below are placed inside the camera body to allowimage-taking. Reference numeral 102 denotes a lens apparatus, in whichan image forming optical system 103 is incorporated and which isattachable/detachable to/from the camera body 101. The lens apparatus102 is electrically and mechanically connected to the camera body 101through a publicly known mounting mechanism.

A plurality of lens apparatuses 102 having different focal lengths areattachable/detachable to/from the camera body 101 and changing the lensapparatus makes it possible to obtain image-taking screens of variousangles of view.

The lens apparatus 102 has a driving mechanism (not shown) and thedriving mechanism can move the focusing lens which is one element of theimage taking optical system 103 in the direction of optical axis L1 tothereby perform focusing. Here, it is also possible to form the focusinglens of a flexible transparent elastic member or liquid lens and performfocusing by changing the interface shape and changing the refractivepower thereof.

Furthermore, a stop (not shown) which adjusts the light quantity of animage-taking light flux by changing the aperture area of an openingthrough which light passes and a driving mechanism (not shown) whichdrives the stop are arranged in the lens apparatus 102.

Reference numeral 106 denotes an image pickup element housed in apackage 124. In the optical path from the image taking optical system103 to the image pickup element 106, an optical low pass filter 156which constrains the cutoff frequency of the image taking optical system103 is provided to repress an unnecessarily high spatial frequencycomponent of the object image from being transmitted on the image pickupelement 106. Furthermore, an infrared cutoff filter is also formed inthe image taking optical system 103.

An object image captured by the image pickup element 106 is displayed ona display unit (image display unit) 107. The display unit 107 isprovided on the back face of the camera body 101 to allow the user todirectly observe the image displayed on the display unit 107. Here, ifthe display unit 107 is made up of an organic EL spatial modulationelement, a liquid crystal spatial modulation element or a spatialmodulation element using particle electrophoresis, etc., it is possibleto reduce power consumption and slim down the display unit.

The image pickup element 106 is a CMOS process compatible sensor (CMOSsensor) which is an amplification type solid-state image pickup element.One of features of the CMOS sensor is the ability to form peripheralcircuits such as a MOS transistor of the area sensor section, an imagepickup element driving circuit, an AD conversion circuit, an imageprocessing circuit in the same step, and therefore the CMOS sensor candrastically reduce the number of masks and process steps compared to aCCD. Furthermore, it has a feature of being able to randomly accessarbitrary pixels, easily read only selected parts to be shown on thedisplay and provide real-time displays at a high display rate.

The image pickup element 106 performs a display image output operationand a high definition image output operation taking advantage of theabove described feature.

Reference numeral 111 denotes a half mirror (first mirror or mirrormember), which leads part of a light flux from the image taking opticalsystem 103 to a view finder optical system (pentaprism 112 or eye piecelens 109), allows the rest of the light flux to pass and thereby dividesone optical path into two optical paths. The half mirror 111 is of amovable type, placed diagonally on the image-taking optical path (on L1)or withdrawn from the image-taking optical path. Reference numeral 105denotes a focusing screen placed on a planned image formation plane ofthe object image. Reference numeral 112 denotes a pentaprism, whichreflects (converts to an erect image) the light flux from the halfmirror 111 a plurality of times and guides it to the eye piece lens 109.

Reference numeral 109 denotes an eye piece lens for observing the objectimage formed on the focusing screen 105 which actually has three lenses(109 a, 109 b, 109 c in FIG. 1) as will be described later. The focusingscreen 105, the pentaprism 112 and the eye piece lens 109 constitute aview finder optical system.

The half mirror 111 has a refractive index of approximately 1.5 and athickness of 0.5 mm. A movable type sub-mirror (second mirror) 122 isprovided behind the half mirror 111 (on the image pickup element 106side) to reflect the light flux close to the optical axis L1 out of thelight flux which has passed through the half mirror 111 toward a focusdetection unit 121.

The sub-mirror 122 is rotatable around a rotation shaft 125 (in FIG. 1)which will be described later and is interlocked with the motion of thehalf mirror 111. Then, the sub-mirror 122 is housed in the lower part ofa mirror box which holds the half mirror 111 and sub-mirror 122 in asecond optical path state and a third optical path state which will bedescribed later.

Reference numeral 104 denotes a movable type illumination unit whichirradiates the object with illumination light and protrudes from thecamera body 101 when used or housed in the camera body 101 when notused.

Reference numeral 113 denotes a focal plane shutter (hereinafterreferred to as “shutter”) which is provided with a front curtain andrear curtain made up of a plurality of light-blocking blades. When noimage is taken, the shutter 113 covers the aperture which constitutes alight passing port with the front curtain or rear curtain to block theimage-taking light flux. When an image is taken, the shutter 113 causesthe front curtain and rear curtain to form slits and run to allow theimage-taking light flux to pass to the image plane side.

Reference numeral 119 denotes a main switch to start the camera. 120denotes a release button which allows a two-stage pressing operation,starts an image-taking preparation operation (a focusing operation and aphotometric operation, etc.) in a half depressed state and starts animage-taking operation in a fully depressed state. Reference numeral 121denotes a focus detection unit which detects a focusing state accordingto a phase difference detection system.

Reference numeral 123 denotes a view finder mode changeover switch andoperating the switch 123 allows the settings of the optical view findermode (OVF mode) and electric view finder mode (EVF mode) to be changed.Here, the OVF mode allows the object image to be observed through theview finder optical system and the EVF mode allows the object image tobe observed through the display unit 107.

Reference numeral 180 denotes an optical view finder internalinformation display unit (information display unit) and causespredetermined information (e.g., image-taking information) to bedisplayed on the focusing screen 105. This allows the photographer tolook into the eye piece lens 109 and thereby observe the object imageand predetermined information.

In the above described structure, as will be described later, the halfmirror 111 and sub-mirror 122 can selectively take three states of afirst optical path state (first state) to guide light to the view finderoptical system and focus detection unit 121, a second optical path state(second state) to guide light to the image pickup element 106 and focusdetection unit 121 and a third optical path state (third state) to allowthe image pickup element 106 to directly receive light from the imagetaking optical system 103.

In the first optical path state, both the half mirror 111 and sub-mirror122 are placed on the diagonal in the image-taking optical path, lightfrom the image taking optical system 103 is reflected by the half mirror111 and guided to the view finder optical system and light which haspassed through the half mirror 111 is reflected by the sub-mirror 122and guided to the focus detection unit 121. In this way, in the firstoptical path state, it is possible to observe the object image throughthe eye piece lens 109 and perform focus detection at the focusdetection unit 121.

In the second optical path state, only the half mirror 111 is placed onthe diagonal in the image-taking optical path and light from the imagetaking optical system 103 is reflected by the half mirror 111 and guidedto the focus detection unit 121 and the light which has passed throughthe half mirror 111 can reach the image pickup element 106. Thesub-mirror 122 is withdrawn from the image-taking optical path.

In this way, in the second optical path state, it is possible to displayan image obtained using the image pickup element 106 on the display unit107, perform image-taking (continuous image-taking or movingimage-taking) and perform focus detection at the focus detection unit121.

In the third optical path state, the half mirror 111 and sub-mirror 122are withdrawn from the image-taking optical path and light from theimage taking optical system 103 can directly reach the image pickupelement 106. In this way, in the third optical path state, it ispossible to perform image-taking or display the image obtained using theimage pickup element 106 on the display unit 107. This image-taking inthe third optical path state allows a high definition image to begenerated and is particularly suitable for a case where the image whichhas been taken is expanded or subjected to large-size printing, etc.

The half mirror 111 is made of transparent resin and designed to weighless to be able to change between the above described three optical pathstates at high speed. Furthermore, a polymer thin-film havingbirefringence is pasted to the back of the half mirror 111. For thisreason, in the second optical path state when the image which has beentaken is monitored using the display unit 107 or a high-speed continuousimage-taking is performed, a stronger low pass effect is provided inresponse to a case where image pickup is not performed using all pixelsof the image pickup element 106.

Furthermore, by forming a micro pyramidal periodic structure having apitch smaller than the wavelength of visible light of resin on thesurface of the half mirror 111, causing it to act as a photonic crystal,it is possible to reduce surface reflection of light due to a refractiveindex difference between air and resin and thereby improve theutilization efficiency of light. This structure can suppress any ghostfrom being produced due to multiple reflection of light on the front andback of the half mirror 111 in the second optical path state.

A mirror driving mechanism having an electromagnetic motor and geartrain (not shown) changes the positions of the half mirror 111 andsub-mirror 122 and thereby changes the optical path state between thefirst optical path state, the second optical path state and the thirdoptical path state.

In the image pickup of the second optical path state, the half mirror111 and sub-mirror 122 are held at predetermined positions as will bedescribed later and there is no need to operate the mirror drivingmechanism, and therefore increasing the image signal processing speedallows ultra-high-speed continuous image-taking. Furthermore, focusingis possible even when an image is displayed on the display unit 107.

FIG. 7 is a block diagram showing an electrical structure of the camerasystem of this embodiment. This camera system has an image pickupsystem, an image processing system, a recording/reproduction system anda control system. First, image pickup and recording of an object imagewill be explained. In FIG. 7, the same members as the members explainedin FIG. 6 are assigned the same reference numerals.

The image pickup system includes the image taking optical system 103 andimage pickup element 106 and the image processing system includes an A/Dconverter 130, an RGB image processing circuit 131 and a YC processingcircuit 132. Furthermore, the recording/reproduction system includes arecording processing circuit 133 and a reproduction processing circuit134 and the control system includes a camera system control circuit(control circuit) 135, an operation detection circuit 136 and an imagepickup element driving circuit 137.

Reference numeral 138 is a connection terminal standardized to beconnected to an external computer, etc., to perform datatransmission/reception. The above described electric circuit is drivenby a small fuel cell (not shown).

The image pickup system is an optical processing system which forms animage of light from an object on an image pickup plane of the imagepickup element 106 through the image taking optical system 103, adjuststhe driving of a stop 143 in the lens apparatus 102 and the frontcurtain and rear curtain of the shutter 113 if necessary and allows theimage pickup element 106 to be exposed to the object light ofappropriate light quantity.

The image pickup element 106 consists of 3700 and 2800 square pixelsarranged in the long side direction and in the short side directionrespectively, approximately 10 million pixels in total, with each pixelprovided with R (red), G (green) and B (blue) color filters alternatelyarranged, four pixels forming one set, that is, a Bayer array.

In the Bayer array, the number of G pixels which are likely to appealmore strongly to the eyes of the photographer is more than the number ofR and B pixels respectively and thereby comprehensive image performanceis improved. Generally, in image processing using the image pickupelement 106 having the Bayer array, luminance signals are generated fromG and color signals are principally generated from R, G and B.

The image signal read from the image pickup element 106 is supplied tothe image processing system through the A/D converter 130. The A/Dconverter 130 is a signal conversion circuit which converts an analogsignal to, for example, a 10-bit digital signal and outputs it accordingto the amplitude of a signal of each pixel exposed to light andsubsequent image signal processing is performed by digital processing.

The image processing system is a signal processing system which obtainsan image signal of a desired format from R, G, B digital signals andconverts R, G, B color signals to luminance signal Y and YC signalexpressed by color difference signals (R-Y) and (B-Y), etc.

The RGB image processing circuit 131 is a signal processing circuitwhich processes an image signal of 3700×2800 pixels received from theimage pickup element 106 through the A/D converter 130 and is providedwith a white balance circuit, a gamma correction circuit and aninterpolation calculation circuit which increases resolution throughinterpolation calculation.

The YC processing circuit 132 is a signal processing circuit whichgenerates a luminance signal Y and color difference signals R-Y and B-Y.The processing circuit 132 has a high-frequency luminance signalgeneration circuit, which generates a high-frequency luminance signalYH, a low-frequency luminance signal generation circuit which generatesa low-frequency luminance signal YL, and a color difference signalgeneration circuit, which generates color difference signals R-Y andB-Y. The luminance signal Y is formed by combining the high-frequencyluminance signal YH and the low-frequency luminance signal YL.

The recording/reproduction system is a processing system which outputsan image signal to memory (recording medium, not shown) and the displayunit 107. The recording processing circuit 133 performs writingprocessing and reading processing on an image signal to/from the memory.The reproduction processing circuit 134 reproduces the image signal readfrom the memory and outputs the reproduced image signal to the displayunit 107.

Furthermore, the recording processing circuit 133 is provided with acompression/expansion circuit which compresses a YC signal expressing astill image and a moving image according to a predetermined compressionformat (e.g., JPEG format) and expands the compressed data when it isread. The compression/expansion circuit includes a frame memory forsignal processing, etc., and stores the YC signal from the imageprocessing system in the frame memory for each frame, reads the YCsignal for every plurality of blocks and compresses and codes the YCsignal. Compression and coding are performed by applying two-dimensionalorthogonal conversion, normalization and Huffman coding to the imagesignal for each block, etc.

The reproduction processing circuit 134 is a circuit which converts theluminance signal Y and color difference signals R-Y and B-Y by a matrixconversion and for example, generates RGB signals. The signals convertedby the reproduction processing circuit 134 are output to the displayunit 107 and visible images are displayed (reproduced) on the displayunit 107.

The reproduction processing circuit 134 and display unit 107 can beconnected through a radio communication channel such as Bluetooth andthis structure allows an image picked up by a camera to be monitoredfrom a remote place.

On the other hand, the operation detection circuit 136 which is part ofthe control system detects operations of the release button 120 and theview finder mode changeover switch 123, etc. Furthermore, the camerasystem control circuit 135 controls the driving of each member in thecamera including the half mirror 111 and the sub-mirror 122 according tothe detection signal of the operation detection circuit 136, generatesand outputs a timing signal when an image pickup operation is performed.

The image pickup element driving circuit 137 generates a driving signalwhich drives the image pickup element 106 under the control of thecamera system control circuit 135. The information display circuit 142controls the driving of the optical view finder internal informationdisplay unit 180.

The control system controls the driving of each circuit of the imagepickup system, image processing system and recording/reproduction systemaccording to an external operation. For example, the control systemdetects that the release button 120 is depressed, controls the drivingof the image pickup element 106, operation of the RGB image processingcircuit 131 and compression processing of the recording processingcircuit 133, etc. Furthermore, the control system controls the state ofeach segment in the information displayed in the optical view finder bya view finder internal information display circuit 142.

Then, the focusing will be explained. An AF control circuit 140 and lenssystem control circuit 141 are connected to the camera system controlcircuit 135. These control circuits communicate data necessary forvarious types of processing with each other centered on the camerasystem control circuit 135.

The AF control circuit 140 generates a focus detection signal byreceiving the output signal of a focus detection sensor 167corresponding to the focus detection area provided at a predeterminedposition on the image-taking screen and detects the in-focus state(defocus amount) of the image taking optical system 103.

When the defocus amount is detected, this defocus amount is converted toan amount of driving of the focusing lens, which is an element of theimage taking optical system 103, and is sent to the lens system controlcircuit 141 through the camera system control circuit 135.

With regard to a moving object, considering a time lag after the releasebutton 120 is depressed until the actual image pickup operation isstarted, an amount of driving of the focusing lens is calculated basedon the result of predicting an appropriate lens stopping position.Furthermore, when it is decided based on a detection result of aluminance detection unit (not shown) which detects the luminance of theobject and is provided in the camera body 101, that the luminance of theobject is low and sufficient focus detection accuracy is not obtained,the object is illuminated using the illumination unit 104 or using awhite LED or a fluorescent tube (not shown) provided in the camera body101.

When the lens system control circuit 141 receives the data showing theamount of driving of the focusing lens sent from the camera systemcontrol circuit 135, it performs an operation, such as moving thefocusing lens using a driving mechanism (not shown) in the lensapparatus 102, in the direction of the optical axis L1 to realizefocusing.

When the AF control circuit 140 detects that focus is achieved on theobject, this detection information is transmitted to the camera systemcontrol circuit 135. At this time, if the release button 120 isdepressed, the processing operation as described above is performed bythe image pickup system, image processing system andrecording/reproduction system.

The stop 143 adjusts a quantity of the object light directed to theimage plane side according to a command from the lens system controlcircuit 141. A communication exchanged between the camera system controlcircuit 135 and the lens system control circuit 141 is performed throughan electric contact (communication unit) 144 a provided on a mountportion of a lens apparatus 102 and an electric contact 144 b providedon a mount portion of a camera body 101.

FIG. 1 to FIG. 5 are longitudinal sectional views of the camera systemof this embodiment. The lens apparatus 102 is only partially shown.These figures principally show operations of the driving mechanisms(mirror driving mechanisms) of the half mirror 111 and sub-mirror 122 ona time-series basis. The same members as the members explained in FIG. 6and FIG. 7 are assigned the same reference numerals.

The structure of the mirror driving mechanism will be explained usingFIG. 3. FIG. 3 shows a view when the camera is in the above describedfirst optical path state.

In FIG. 3, reference numeral 101 denotes a camera body, referencenumeral 102 denotes a lens apparatus, reference numeral 103 a denotes alens located closest to the image plane out of a plurality of lensesmaking up the image taking optical system, reference numeral 105 denotesa focusing screen of a view finder optical system. Reference numeral 164denotes a condenser lens which serves as a window for taking in a lightflux of a focus detection unit 121 and reference numeral 107 denotes adisplay unit. Reference numeral 163 denotes an eye piece shutter(light-blocking member) which can move with respect to the optical pathof the view finder optical system. The eye piece shutter is the memberwhich suppresses an adverse effect on image pickup due to the light fromthe eye piece lens 109 side.

A movable type half mirror 111 is supported by a half mirror receivingplate (not shown). The half mirror receiving plate is provided with pins173 and 174, and the half mirror 111 and pins 173 and 174 are unifiedthrough the half mirror receiving plate and are movable.

Reference numeral 170 denotes a half mirror driving lever, referencenumeral 171 denotes a half mirror support arm. The half mirror drivinglever 170 is supported to a rotation shaft 170 a in a rotatable mannerand the half mirror support arm 171 is supported by a rotation shaft 171a in a rotatable manner.

The half mirror driving lever 170 is connected to a drive source througha power transmission mechanism (not shown) and can rotate around therotation shaft 170 a by receiving a driving force from the drive source.Furthermore, the half mirror support arm 171 is connected to a member ofsubstantially the same shape on the facing wall side of a mirror boxthrough a connection portion 171 b.

A pin 173 provided on the half mirror receiving plate (not shown) isfitted into a through hole portion 171 c provided at the end of the halfmirror support arm 171 in a slidable manner. This allows the half mirror111 to rotate around the through hole portion 171 c (pin 173) throughthe half mirror receiving plate. Furthermore, a spring force by atorsion spring (not shown) in the direction shown by an arrow A isapplied to a position intermediate between the pins 173 and the pin 174of the half mirror receiving plate.

In the first optical path state (FIG. 3), mirror stoppers (stoppermembers) 160 and 161 are outside the image-taking optical path andinside the range of the moving track of the half mirror 111. Byreceiving the spring force of the torsion spring in the directionindicated by the arrow A in the state shown in FIG. 3, the half mirror111 contacts the mirror stoppers 160 and 161 and is positioned. Thiscauses the half mirror 111 to be placed on the diagonal in theimage-taking optical path.

Here, the pin 173 does not contact a first cam face 170 b of the halfmirror driving lever 170 and the pin 174 does not contact a second camface 170 c of the half mirror driving lever 170.

Furthermore, the sub-mirror 122 is positioned on the back of the halfmirror 111 with its rotation around a rotation shaft 125 suppressed.

In the first optical path state, the light flux reflected by the halfmirror 111 out of the light fluxes which have passed through the imagetaking optical system 103 (lens 103 a) is guided to the view finderoptical system and the light flux which has passed through the halfmirror 111 is reflected by the sub-mirror 122 behind the half mirror 111and guided to the focus detection unit 121.

When the mirror stoppers 160 and 161 are withdrawn from the range of themoving track of the half mirror 111 or when the half mirror drivinglever 170 rotates clockwise in FIG. 3, the pin 173 contacts the firstcam face 170 b of the half mirror driving lever 170 and the pin 174contacts the second cam face 170 c of the half mirror driving lever 170through the spring force of the torsion spring (not shown) in thedirection indicated by the arrow A.

Then, the pins 173 and 174 move along the first cam face 170 b and thesecond cam face 170 c according to the amount of rotation of the halfmirror driving lever 170. This changes the posture of the half mirror111.

That is, the half mirror receiving arm 171 rotates in connection withthe rotation of the half mirror driving lever 170. Then, the half mirrorsupport plate connected to the half mirror driving lever 170 and thehalf mirror support arm 171 through the pins 173 and 174 operates andthe half mirror 111 operates together with the half mirror receivingplate.

FIG. 1 to FIG. 5 show operations of the half mirror 111 and thesub-mirror 122. FIG. 1 shows the above described second optical pathstate, FIG. 2 shows a partway transition from the first optical pathstate to the second optical path state. FIG. 4 shows a process oftransition from the first optical path state to the third optical pathstate and FIG. 5 shows the above described third optical path state.

In the first optical path state (FIG. 3), as described above, the halfmirror 111 and the sub-mirror 122 operate so as to guide the objectlight emitted from the image taking optical system 103 to the viewfinder optical system and the focus detection unit 121.

In the second optical path state (FIG. 1), the half mirror 111 operatesso as to guide the object light emitted from the image taking opticalsystem 103 to the image pickup element 106 and the focus detection unit121. Furthermore, in the third optical path state (FIG. 5), the halfmirror 111 and the sub-mirror 122 withdraw from the image-taking opticalpath.

Then, an image-taking sequence in the camera system of this embodimentwill be explained using FIG. 8 below.

In step S1, the process waits until the main switch 119 is operated (ONstate) and advances to step S2 when operated. In step S2, a current issupplied to various electric circuits in the camera body 101.

In step S3, the set view finder mode is identified and if an OVF mode isset, the process advances to step S4, and if an EVF mode is set, theprocess advances to step S5.

In step S4, predetermined information is displayed on the displaysection provided in the optical view finder by driving the optical viewfinder internal information display unit 180. In the OVF mode, it ispossible to observe not only the above described predeterminedinformation but also the object image through the eye piece lens 109.

In step S5, an image and predetermined information are displayed on thedisplay unit 107. In the EVF mode, it is possible to observe not onlythe above described predetermined information but also the object imagethrough the display unit 107.

Here, when the operation detection circuit 136 detects that the viewfinder mode changeover switch 123 has been operated, the view findermode is changed. For example, when the OVF mode is changed to the EVFmode, an image (object image) is displayed on the display unit 107through the driving of the image pickup system and the image processingsystem.

In step S6, the process waits until it is detected that the releasebutton 120 is half depressed based on the output of the operationdetection circuit 136, that is, until SW1 is put in an ON state andadvances to step S7 when SW1 is put in an ON state.

In step S7, the luminance of the object is measured (photometricoperation) and the focus detection unit 121 detects the focusing stateaccording to a phase difference detection system (focus detectionoperation).

These detection results obtained in step S7 are sent to the camerasystem control circuit 135 and an exposure value (shutter speed and stopvalue) and defocus amount are calculated. Then, based on the calculateddefocus amount, the focusing lens of the image taking optical system 103is driven for focusing under the control of the AF control circuit 140and the lens system control circuit 141. Furthermore, a stop (not shown)is driven based on the calculated stop value and the area of theaperture through which the light passes is changed.

In step S8, based on the output of the operation detection circuit 136,the camera system control circuit 135 decides whether the release button120 has been fully depressed or not, that is, whether SW2 is in an ONstate or not. Here, if SW2 is in an ON state, the process advances on tostep S9, and if SW2 is in an OFF state, the process returns to step S6.

In step S9, the half mirror 111 and the sub-mirror 122 are put in thethird optical path state (FIG. 5) by driving the mirror drivingmechanism. In step S10, the image pickup element 106 is exposed to lightby operating the shutter 113 based on the shutter speed calculatedbefore and in step S11, the image processing system captures a highdefinition image.

Here, the above described image-taking sequence applies to a case wherea high definition image is taken and the sequence in a case wherehigh-speed continuous image-taking is performed partially differs fromthe above described sequence. That is, the half mirror 111 and thesub-mirror 122 are in the second optical path state (FIG. 1) and theaperture of the shutter 113 remains open.

In the second optical path state, the light flux from the image takingoptical system 103 is divided into the component to be reflected to thefocus detection unit 121 by the half mirror 111 and the component whichpasses through the half mirror 111. Then, an image is taken when thecomponent which has passed through the half mirror 111 is received bythe image pickup element 106. When continuous image-taking is performed,the mirror driving mechanism is not driven, and therefore the halfmirror 111 is held in the same state (state in FIG. 1).

The camera of this embodiment is structured in such a way that even whenthe image picked up is monitored on the display unit 107, a high-speedfocusing operation (driving of the focusing lens) can be performed bydetecting the focusing state according to the phase difference detectionsystem through the focus detection unit 121.

Then, the changeover operation between the view finder modes will beexplained.

While the electric circuit in the camera is operating, the state(ON/OFF) of each operation switch is detected through the operationdetection circuit 136 and when it is detected that the view finder modechangeover switch 123 has been operated, the changeover operation of theview finder mode (OVF mode and EVF mode) is started immediately (step S3in FIG. 8).

FIG. 9 is a flow chart illustrating the changeover operation of the viewfinder mode and this operation will be explained below according to thisflow.

In step S100, the actual view finder mode is detected, and when the OVFmode is changed to the EVF mode through the operation of the view findermode changeover switch 123, the process advances on to step S101. On theother hand, when the EVF mode is changed to the OVF mode, through theoperation of the view finder mode changeover switch 123, the processadvances on to step S111.

First, the case where the OVF mode is changed to the EVF mode will beexplained.

In the OVF mode, the optical path splitting system, including the halfmirror 111 and the sub-mirror 122, is in the first optical path state(FIG. 3). In the EVF mode, the object light is not guided to the opticalview finder, and therefore in step S101, the camera system controlcircuit 135 drives the drive source (not shown) to thereby close the eyepiece shutter 163 first. That is, the eye piece shutter 163 is insertedin the view finder optical path between the lens 109 b and lens 109 c.

This is intended to prevent the photographer from mistaking a phenomenonthat the object image can not be observed invisible through the eyepiece lens 109 when the EVF mode is set, for a camera failure andrepress inverse incident light from the optical view finder fromentering the image pickup element 106 and thereby causing a ghost imageto be produced.

In step S102, information in the optical view finder is in a non-displaystate through the driving control of the view finder internalinformation display unit 180. This is because the eye piece shutter 163is already closed in step S101 and even if information is displayed inthe optical view finder, the photographer cannot see this display. Thismakes it possible to reduce power consumption and suppress consumptionof the battery.

In step S103, the mirror driving mechanism is operated and thesub-mirror 122 is thereby withdrawn to the lower part of the mirror box(FIG. 1) in preparation for changing the state of the half mirror 111 tothe second optical path state (FIG. 1).

In step S104, the mirror stoppers 160 and 161 are withdrawn from themoving track of the half mirror 111. After the mirror stoppers 160 and161 are withdrawn, in step S105, the half mirror driving lever 170 isrotated counterclockwise in FIG. 3 through the mirror driving mechanism.The half mirror 111 receives the spring force of the torsion spring (notshown) in the direction indicated by the arrow A and is thereby changedthrough the state shown in FIG. 2 to the second optical path state (FIG.1).

When the half mirror 111 is in the second optical path state, part ofthe light flux from the image taking optical system 103 is reflected bythe half mirror 111 and guided to the focus detection unit 121.Furthermore, the remaining light flux passes through the half mirror 111and is directed to the image pickup element 106.

In the second optical path state, the half mirror 111 receives thespring force of the torsion spring in the direction indicated by thearrow A, contacts the mirror stoppers 175 and 176 located outside theimage-taking optical path and is thereby positioned. At this time, thepin 173 does not contact the first cam face 170 b of the half mirrordriving lever 170 and the pin 174 does not contact the second cam face170 c of the half mirror driving lever 170.

The position of the reflecting surface of the half mirror 111 is theposition at which the reflecting surface of the sub-mirror 122 in thefirst optical path state is located. Such a structure makes it possibleto eliminate a difference between the light reflected by the sub-mirror122 (in the first optical path state) and guided to the focus detectionunit 121, and the light reflected by the half mirror 111 (in the secondoptical path state) and guided to the focus detection unit 121, andprevent the position of the focus detection area from changing at all.

Here, the focusing position of the object image formed by the light fluxwhich has passed through the half mirror 111 may be slightly deviatedfrom the focusing position in a case where object light does not passthrough the half mirror 111. For this reason, in step S106, a focusingcorrection mode is started to correct the deviation of the focusingposition.

In the first optical path state, when the image taking optical system103 is in the in-focus state and the half mirror 111 and sub-mirror 122are withdrawn from the image-taking optical path (in the third opticalpath state), the focus detection unit 121 outputs a focus detectionsignal so that the object image is formed sharply on the image pickupelement 106.

In contrast, when the image taking optical system 103 is in the in-focusstate and the focusing correction mode is set in the second optical pathstate, the focus detection signal of the focus detection unit 121 iscorrected so that the object image which has passed through the halfmirror 111 and has been projected onto the image pickup element 106 isformed sharply. When the focusing correction mode is set in the secondoptical path state, this causes the in-focus position of the focusinglens in the second optical path state to be deviated from the in-focusposition of the focusing lens in the third optical path state by theamount of correction of the focus detection signal of the focusdetection unit 121.

Therefore, while the EVF mode is set, when the release button 120 isfully depressed, the image pickup operation is started and the secondoptical path state is changed to the third optical path state, the frontcurtain driving mechanism of the shutter 113 is charged (the shutter 113is closed) in synchronization with the above described change of theoptical path state and the focusing lens is returned to the originalposition (in-focus position in the third optical path state) by theamount of correction of the focusing position of the object image in thefocusing correction mode. Then, the shutter 113 is opened for apredetermined time and an image is picked up through the image pickupelement 106.

This structure makes it possible to exactly check the focusing statebased on the image displayed on the display unit 107 in the secondoptical path state and then pick up an image focused in the thirdoptical path state.

In step S107, only the front curtain of the shutter 113 is run to createa bulb exposure state and the object light is guided continuously to theimage pickup element 116, thereby making it possible for the imagepickup to display the image on the display unit 107. In step S108, thepower to the display unit 107 is turned on.

In step S109, object images are picked up consecutively using the imagepickup element 106, display on the display unit 107 in real time isstarted, and a series of view finder changeover processes is returned.

In the EVF mode (second optical path state), the object light passedthrough the image taking optical system 103 may receive a refractiveaction by the half mirror 111, and therefore the electronic image of theobject displayed on the display unit 107 in real time is slightlydeviated upward or downward compared to the image actually picked up inthe third optical path state.

FIG. 12 illustrates a difference between the image displayed on thedisplay unit 107 in the second optical path state and the image actuallytaken in the third optical path state.

In FIG. 12, reference numeral 190 denotes an image pickup range in whichan image is picked up in the second optical path state (area enclosed bya bold frame), that is, the range of the image taken which can be outputto the display unit 107 in a real-time display. Reference numeral 191denotes an image pickup range in which an image is picked up in thethird optical path state.

The image pickup range 190 and the image pickup range 191 are shiftedupward or downward from each other, and as a result, there is an area190 a which can be output to the display unit 107 but is not picked upin the third optical path state, that is, the area of the image pickuprange 190 which does not overlap with the image pickup range 191.

Thus, as shown in FIG. 13, the reproduction processing circuit 134 hidesthe area 192 which corresponds to the area 190 a in FIG. 12 and performsprocessing so that the entire image-taking range 190 is not displayed onthe display unit 107. This causes the image pickup area 190 excludingthe area 192 (corresponds to the partial area in the claim) to bedisplayed on the display unit 107. This makes it possible to eliminatethe problem that even if the image is displayed on the display unit 107in the EVF mode, the image is actually not taken.

Then, a case where the process advances on to step S111 to change itsmode from the EVF mode to OVF mode based on a decision of the viewfinder mode in step S100 will be explained.

In the initial state EVF mode, the optical path splitting systemincluding the half mirror 111 and the sub-mirror 122 is in the secondoptical path state (FIG. 1) and a real-time display is performed on thedisplay unit 107 as described above.

In step S111, the power to the display unit 107 is turned off and imagepickup using the image pickup element 106 is stopped. In step S112, therear curtain of the shutter 113 is run to close the aperture of theshutter 113 and the front curtain/rear curtain driving mechanism ischarged in preparation for image-taking.

In step S113, to allow the movement of the half mirror 111, the mirrorstoppers 160 and 161 are withdrawn from the moving track of the halfmirror 111.

In step S114, the half mirror driving lever 170 is rotated clockwise inFIG. 1, and thereby moving the half mirror 111 and the sub-mirror 122,which make up the optical path splitting system, from the state in FIG.2→state in FIG. 3→state in FIG. 4→state in FIG. 5 (third optical pathstate).

When the half mirror driving lever 170 rotates clockwise, the pin 174 ispushed by the second cam face 170 c and moved and the pin 173 is pushedby the first cam face 170 b and moved. Thus, the half mirror support arm171 rotates around the rotation shaft 171 a clockwise and the halfmirror 111 rotates around the pin 173 clockwise (See FIG. 1 to FIG. 5).

In step S115, the mirror stoppers 160 and 161 are inserted in the rangeof the moving track of the half mirror 111.

After the half mirror 111 is moved to the third optical path state, themirror stoppers 160 and 161 are inserted, and therefore the insertedmirror stoppers 160 and 161 do not collide with the half mirror 111.This makes it possible to improve structural reliability of the cameraof this embodiment when the position of the half mirror 111 is changed(switching between OVF mode and EVF mode).

According to Embodiment 1, the half mirror 111 is moved to the thirdoptical path state, but as far as the mirror stoppers 160 and 161 do notcollide with the half mirror 111, the half mirror 111 may also be movedto the vicinity of the position of the third optical path state.

In step S116, the half mirror 111 is changed from the third optical pathstate (FIG. 5) to the state in FIG. 4 and finally the first optical pathstate (FIG. 3) by turning the half mirror driving lever 170counterclockwise in FIG. 5. At this time, the half mirror 111 receivesthe spring force of the spring (not shown) in the mirror drivingmechanism and remains in contact with the mirror stoppers 160 and 161.

In step S117, the eye piece shutter 163 is opened.

In step S118, the camera system control circuit 135 decides based on theoutput from the operation detection circuit 136 whether a manual (M)focus mode is set or not, and if the manual focus mode is set, theprocess advances on to step S107 and if an auto focus mode is setinstead of the manual focus mode, the process advances on to step 120.

In the case of the manual focus mode, the focus detection unit 121 neednot be operated, the degree of blurring of the background can berecognized more accurately with the electronic image display than theoptical view finder, and therefore the process advances on to step S107and a real-time display is performed on the display unit 107.

In step S120, the sub-mirror 122 is set to a predetermined position sothat the object light is guided to the focus detection unit 121. Thatis, the sub-mirror 122 housed in the lower part of the mirror box (FIG.5) is moved behind the half mirror 111 by turning the sub-mirror 122around the rotation shaft 125 (FIG. 3).

In step S121, predetermined information is lit and displayed in the viewfinder under the driving control of the optical view finder internalinformation display unit 180 and a series of view finder changeoverprocessing is terminated.

Then, the constitution of the focus detection unit 121 and signalprocessing for focus detection will be explained.

In FIG. 1 to FIG. 5, reference numeral 164 denotes a condenser lens,reference numeral 165 denotes a reflecting mirror, reference numeral 166denotes re-image formation lens and reference numeral 167 denotes afocus detection sensor.

The light flux passed through the image taking optical system 103, andreflected by the half mirror 111 (in the second optical path state) orby the sub-mirror 122 (in the first optical path state) enters thecondenser lens 164 provided in the lower part of the mirror box, and isdeflected by the reflecting mirror 165 and a secondary image of theobject is formed on the focus detection sensor 167 by the action of there-image formation lens 166.

The focus detection sensor 167 is provided with at least two pixelarrays and a relatively lateral shift is observed according to the imageformation state of the object image formed by the image taking opticalsystem 103 in the focus detection area between the output signalwaveforms of the two pixel arrays. The output signal waveforms in thefront focus and the rear focus shift to the opposite directions, and itis the principle of focus detection (contrast detection system) that thephase difference (amount of shift) is detected including the shiftdirection using a technique such as correlation calculation, etc.

FIG. 10 and FIG. 11 show output signal waveforms of the focus detectionsensor 167 input to the AF control circuit 140. The horizontal axisshows an arrangement of pixels and the vertical axis shows an outputvalue of the focus detection sensor 167. FIG. 10 shows output signalwaveforms when focusing on the object image is not achieved and FIG. 11shows output signal waveforms when focusing on the object image isachieved.

Light beams for focus detection are generally not the same as the imageformation beams when the stop is released and focus detection isperformed using part of the image formation beams. That is, light beamsof a dark F number are used for focus detection. Furthermore,considering errors in the mechanism, the position of the image pickupelement 106 cannot be optically conjugate with the position of the focusdetection sensor 167 in the strict sense. As a result, even if focusingon the object image is achieved, a small initial phase difference Δbetween two output signal waveforms remains (FIG. 11).

This is different from the correction in the above described focusingcorrection mode to make the electronic displayed image sharp (step S106in FIG. 9). A true phase difference can be obtained by subtracting theinitial phase difference from the phase difference detected by thecalculation of correlation between two images, and therefore theexistence of the initial phase difference Δ itself normally causes noproblem.

However, there is a problem that the position of the reflecting surfaceof the sub-mirror 122 in the first optical path state does notcompletely match the position of the reflecting surface of the halfmirror 111 in the second optical path state in terms of the accuracy ofthe mechanism and the initial phase difference Δ also differs slightly.With normal parts machining accuracy, the position of the reflectingsurface may deviate in the direction of the normal of the reflectingsurface by approximately 30 μm and reducing this amount increases themachining cost of parts considerably.

Thus, an initial phase difference Δ is set in advance for each of thefirst optical path state and second optical path state and the value ofthe initial phase difference Δ is changed according to the optical pathstate. For example, the initial phase differences Δ in the first opticalpath state and the second optical path state are stored in a memory 135a provided in the camera system control circuit 135. Then, by detectingthe position of the mirror (half mirror 111 and sub-mirror 122) ordetecting the view finder mode (EVF mode and OVF mode), it is possibleto read the initial phase differences Δ in the first optical path stateand the second optical path state from the memory 135 a.

Adopting such a structure allows focus detection to be performed with ahigh degree of accuracy in any optical path state.

Thus, using the concept of an initial phase difference, it is possibleto detect an in-focus state by deciding the identity of a set ofsignals. Furthermore, by detecting a phase difference using a publiclyknown technique using a correlation calculation, for example, thetechnique disclosed in the above described Document 5, it is possible tocalculate a defocus amount. If the defocus amount obtained is convertedto the amount of driving the focusing lens of the image taking opticalsystem 103, auto focusing is possible.

The above described method allows the amount of driving the focusinglens to be recognized beforehand, driving of the focusing lens to thein-focus position is required almost one time, and extremely high-speedfocusing is possible.

According to the camera system of this embodiment, even when anelectronic image display of an object image is performed on the displayunit 107 in the second optical path state, it is possible to detect afocusing state according to a phase difference detection system by thefocus detection unit 107 as in the case of the first optical path stateand perform a high-speed focusing operation (driving of the focusinglens). Furthermore, by allowing continuous image-taking or movingimage-taking in the second optical path state, it is possible to realizea high-speed focusing operation. Furthermore, it is possible to reducethe size of the camera system compared to the case in above describedDocument 4 where the focus detection unit is provided for both the lensapparatus and camera body and prevent the cost from increasing as well.

In this embodiment, the light passed through the image taking opticalsystem 103 in the second optical path state (FIG. 1) is guided by thehalf mirror 111 to the focus detection unit 121 and the focus detectionunit 121 only detects focusing state according to the phase differencedetection system, but in addition to this, it is also possible to detectfocusing state according to a contrast detection system using the lightwhich has passed through the half mirror 111 and is received by theimage pickup element 106.

For example, it is possible to move the focusing lens by focusingaccording to the phase difference detection system to the vicinity ofthe in-focus position and stop the focusing lens at the in-focusposition by focusing according to the contrast detection system. Thismakes it possible to move the focusing lens to the vicinity of thein-focus position speedily and improve the accuracy of the in-focusposition.

Furthermore, this embodiment has described the camera system having ofthe lens apparatus 102 and camera body 101, but the present invention isalso applicable to a camera constructed of a lens apparatus and camerabody combined in one unit. In this case, the lens system control circuit141 in FIG. 7 is not necessary and the camera system control circuit 135performs a control operation of the lens system control circuit 141.

As described above, a plurality of lens apparatuses 102 having differentfocal lengths are attachable/detachable to/from the camera body 101.Therefore, a different signal is transmitted from the camera systemcontrol circuit 135 depending on whether the lens apparatus 102 isattachable to the camera body 101 of this embodiment or the conventionalcamera body.

That is, in the case where the lens apparatus 102 is attachable to thecamera body 101 which is explained in this embodiment, a communicationexchanged between the camera system control circuit 135 and the lenssystem control circuit 141 is performed to perform a control describedbelow.

The lens system control circuit 141, which has received a signalindicating the second optical path state (a second mode) from the camerasystem control circuit 135, controls the aperture of the stop 143.

Exposure is adjusted to display the image on the display unit (imagedisplay unit) 107 in the case where the camera body 101 of thisembodiment is used. On the other hand, the stop is stopped down toperform a photometry operation and an image-taking operation in the casewhere the conventional camera body is used.

An auto focus operation, in the case where the conventional camera bodyis used and an auto focus operation in the case where the lens systemcontrol circuit 141 receives a signal indicating the first optical pathstate (a first mode) from the camera system control circuit 135 in thecamera system of this embodiment, is performed with a full openedaperture.

On the contrary, in the camera system of this embodiment, a focusoperation of the image-taking optical system 103 according to thedetection result of the focus detection unit 121 is allowed even if thestop 143 is stopped down in the second optical path state.

Furthermore, in the camera system of this embodiment, after the apertureof the stop is changed and the image-taking operation (continuousimage-taking or moving image-taking) is performed, the aperture of thestop 143 is returned to a state for displaying the image on the displayunit 107.

According to this embodiment, when the light flux from the image takingoptical system 103 is guided to the view finder optical system (firstoptical path state) and the image pickup element (second optical pathstate), the light flux is also guided to the focus detection unit 121.This makes it possible to detect the focusing state according to a phasedifference detection system by the focus detection unit 121 not onlywhen an object image is observed through the view finder optical systembut also when the object image is picked up by the image pickup element(e.g., when continuous image-taking or moving image-taking isperformed).

For this reason, when an object image is picked up using the imagepickup element 106, it is possible to perform a focusing operation morequickly than a (conventional) case where a focusing state is detectedaccording to a contrast detection system. Moreover, there is no need toprovide two focus detection units as described in above Document 4, andtherefore it is possible to prevent any increase in size and cost of theapparatus.

Furthermore, even when an image picked up using the image pickup element106 is displayed on the display unit 107 and this image is observed, itis possible to perform the focusing operation quickly as describedabove.

Embodiment 2

A camera system which is Embodiment 2 of the present invention will beexplained.

According to Embodiment 1, the first optical path state is directlychanged to the second optical path state and when the second opticalpath state is changed to the first optical path state, this is donethrough the third optical path state.

On the other hand, according to this embodiment, when a changeover ismade between the first optical path state and the second optical pathstate, this is done through the third optical path state and this is apoint in which Embodiment 2 differs from Embodiment 1. The partsdifferent from those of Embodiment 1 will be explained below.

The rest of the camera structure other than the optical path splittingsystem (half mirror, sub-mirror and mirror driving mechanism) isgenerally the same as the camera structure of Embodiment 1, andtherefore the same members as those explained in Embodiment 1 areassigned the same reference numerals.

FIG. 14 illustrates operations of an optical path splitting systemaccording to this embodiment. FIG. 14(A) illustrates the first opticalpath state, FIG. 14(C) illustrates the third optical path state and FIG.14(E) illustrates the second optical path state. Furthermore, FIG. 14(B)illustrates the process of transition between the first optical pathstate and the third optical path state with its sequential steps shownsimultaneously and FIG. 14(D) illustrates the process of transitionbetween the third optical path state and the second optical path statewith its sequential steps shown simultaneously.

In these figures, reference numeral L2 denotes an optical axis of theimage taking optical system 103, reference numeral 206 denotes an imagepickup element (light receiving surface), reference numeral 211 denotesa movable-type half mirror, reference numeral 222 denotes a sub-mirrorand reference numeral 201 denotes a light-blocking plate. Referencenumeral 202 denotes a mirror stopper which contacts the half mirror 211to hold the half mirror 211 in a first optical path state. Referencenumeral 203 denotes a mirror stopper which contacts the half mirror 211to hold the half mirror 211 in a second optical path state. These mirrorstoppers 202 and 203 are fixed inside the camera body unlike Embodiment1.

In the first optical path state shown in FIG. 14(A), the half mirror 211is placed on the diagonal with respect to the optical axis L2 andpositioned by receiving a spring force of a spring (not shown) andcontacting the mirror stopper 202. Furthermore, a sub-mirror 222 islocated behind the half mirror 211.

The first optical path state is a state in which the OVF mode is set asin the case of Embodiment 1 and it is possible to observe an objectimage through a view finder optical system and detect a focusing stateaccording to a phase difference detection system by a focus detectionunit 121.

A light flux incident on the half mirror 211 from the image takingoptical system 103 located on the left in the figure along the opticalaxis L2 is partially reflected in the upward direction of the camera(upward in the figure) on the surface of the half mirror 211 and guidedto the view finder optical system. On the other hand, the rest of thelight flux passes through the half mirror 211, reflected in the downwarddirection of the camera (downward in the figure) by the sub-mirror 222located behind the half mirror 211 and guided to the focus detectionunit 121.

In the third optical path state shown in FIG. 14(C), the half mirror 211and sub-mirror 222 are withdrawn to positions in the upper part of thecamera so as not to interrupt the image formation light flux. At thistime, the light-blocking plate 201 covers the area of the half mirror211 which does not overlap with the sub-mirror 222 and blocks reverseincident light from the view finder optical system together with thesub-mirror 222. This prevents the reverse incident light from the viewfinder optical system from entering the image pickup element 206 and canthereby prevent any ghost image from occurring.

In the second optical path state shown in FIG. 14(E), the half mirror211 is placed on the diagonal with respect to the optical axis L2 and ispositioned by receiving a spring force of a spring (not shown) andcontacting the mirror stopper 203. On the other hand, the sub-mirror 222is placed in the upper part of the camera together with thelight-blocking plate 201 and withdrawn from the image-taking opticalpath.

The second optical path state is a state in which the EVF mode is set asin the case of Embodiment 1, and it is possible to observe an objectimage through the display unit 107 and the focus detection unit 121 candetect the focusing state according to a phase difference detectionsystem.

The light flux incident on the half mirror 211 from the image takingoptical system 103 located on the left side in the figure along theoptical axis L2 is partially reflected on the back surface of the halfmirror 211 in the downward direction of the camera and guided to thefocus detection unit 121. Furthermore, the rest of the light flux passesthrough the half mirror 211 and enters the image pickup element 206.

The transition from the first optical path state (A) to the thirdoptical path state (C) is substantially the same as a mirror raisingoperation of a general single-lens reflex camera as shown in FIG. 14(B).That is, the half mirror 211 rotates in such a way that its surfacesturns up in the camera and the sub-mirror 222 rotates in such a way thatits reflecting surface turns up in the camera. At this time, thesub-mirror 222 moves to the position along the half mirror 211.

The transition from the third optical path state (C) to the firstoptical path state (A) is an operation opposite to the above describedoperation (from (A) to (C) in FIG. 14). Furthermore, the above describedoperations of the half mirror 211 and sub-mirror 222 can be performedby, for example, transmitting the driving force of the motor to a cammember through a gear train, rotating the cam member and thereby movingpins of the half mirror 211 and sub-mirror which engages with the cammember.

On the other hand, in the transition from the third optical path state(C) to the second optical path state (E), the half mirror 211 locatedsubstantially parallel to the optical axis L2 starts to lower from theback end of the half mirror 211, that is, the side close to the imagepickup element 206 and contacts the mirror stopper 203. At this time,the back surface of the half mirror 211 faces the image taking opticalsystem 103 side.

The position of the half mirror 211 substantially matches the positionof the sub-mirror 222 in the first optical path state. Here, in thisembodiment, unlike Embodiment 1, the reflecting surface of the halfmirror 211 faces the image pickup element 206 side, and therefore theposition of the half mirror 211 is determined in such a way that theoptical axis after deflection by the half mirror 211 matches the opticalaxis of the light incident on the focus detection unit 121 in the firstoptical path state.

Such a structure makes it possible to prevent the position of the focusdetection area from varying between the first optical path state and thesecond optical path state.

According to this embodiment, when the first optical path state and thesecond optical path state are switched, this is done through the statesin FIG. 14(B) to 14(D), and therefore there is no need to make themirror stoppers 202 and 203 movable (structure of moving the mirrorstoppers forward or backward with respect to the moving track of themirror) as in the case of Embodiment 1. Furthermore, the operations ofthe half mirror 211 and sub-mirror 222 are not interrupted by the mirrorstoppers 202 and 203, and therefore it is possible to secure structuralreliability when switching between the first optical path state and thesecond optical path state.

According to the camera system of this embodiment, even when anelectronic image of an object is displayed on the display unit 107 inthe second optical path state, it is possible to detect a focusing stateaccording to a phase difference detection system as in the case of thefirst optical path state, and therefore it is possible to realize ahigh-speed focusing operation (driving of focusing lens). Furthermore,by performing continuous image-taking and moving image-taking in thesecond optical path state, it is possible to perform a high-speedfocusing operation. Moreover, since there is no need to provide a focusdetection unit in the lens apparatus and camera body as in the case ofabove described Document 4, it is possible to reduce the size of thecamera and prevent its cost from increasing.

Embodiment 1 and Embodiment 2 have described the camera for taking colorpictures as an example, but the present invention is not limited to theabove described embodiments and it is also applicable to an infraredimage taking apparatus, monochrome camera or binocular with an imagepickup function, etc.

While preferred embodiments have been described, it is to be understoodthat modification and variation of the present invention may be madewithout departing from scope of the following claims.

1. An image taking apparatus comprising: a light splitting unit whichsplits a light flux from an image-taking lens into a plurality of lightfluxes; a view finder optical system configured and positioned toobserve an object image formed by the light flux from the image-takinglens; an image pickup element which photoelectrically converts theobject image to an electrical signal; and a focus detection unitconfigured and positioned to detect the focusing state of theimage-taking lens according to a phase difference detection system,wherein the light splitting unit changes its state among a first statein which the light flux is directed to the view finder optical systemand the focus detection unit, a second state in which the light flux isdirected to the image pickup element and the focus detection unit and athird state in which the light flux is directed only to the image pickupelement, wherein the light splitting unit has a half mirror and areflection mirror which prevents an incident light flux from passingthrough the reflection mirror wherein in the first state, the halfmirror and the reflection mirror are positioned in an image-takingoptical path so that part of the light flux is reflected by the halfmirror and directed to the view finder optical system, and the rest ofthe light flux a) passes through the half mirror, b) is reflected by thereflection mirror, and c) is directed to the focus detection unit, andwherein in the second state, the reflection mirror is withdrawn from theimage-taking optical path and the orientation of the reflecting surfaceof the half mirror is changed in the image-taking optical path withrespect to the first state so that part of the light flux is reflectedby the half mirror and directed to the focus detection unit, and therest of the light flux passes through the half mirror and is directed tothe image pickup element, and wherein in the third state, the halfmirror and the reflection mirror are withdrawn from the image-takingoptical path so that the light flux is directed only to the image pickupelement.
 2. The image taking apparatus according to claim 1, furthercomprising: an image display unit which displays image data acquiredusing the image pickup element; and a control circuit which controls thedriving of the image display unit, wherein the control circuit causesthe image display unit to display the image data when the lightsplitting unit is in the second state.
 3. The image taking apparatusaccording to claim 2, wherein the control circuit causes the imagedisplay unit to display only a part of the image data when the lightsplitting unit is in the second state.
 4. The image taking apparatusaccording to claim 1, further comprising: an information display unitwhich displays information within the field of view of the view finderoptical system; and a control circuit which controls the driving of theinformation display unit, wherein the control circuit does not drive theinformation display unit when the light splitting unit is in the secondstate.
 5. The image taking apparatus according to claim 1, furthercomprising: a light-blocking member which moves with respect to theoptical path of the view finder optical system; and a control circuitwhich controls the driving of the light-blocking member, wherein thecontrol circuit causes the light-blocking member to be inserted into theoptical path of the view finder optical system when the light splittingunit is in the second state.
 6. The image taking apparatus according toclaim 1, further comprising: a control circuit which determines thefocusing state of the image-taking lens based on the output of the focusdetection unit, wherein the control circuit changes the determination ofthe focusing state according to the first state and the second state. 7.The image taking apparatus according to claim 6, wherein the controlcircuit determines the focusing state by correcting the output of thefocus detection unit based on an initial phase difference and changesthe value of the initial phase difference according to the first stateand the second state.
 8. The image taking apparatus according to claim1, wherein the position of the reflecting surface of the reflectionmirror in the first state is substantially the same as the position ofthe reflecting surface of the half mirror in the second state.
 9. Theimage taking apparatus according to claim 1, wherein when changing fromone state to the other between the first state and the second state, thelight splitting unit is placed in the third state.
 10. The image takingapparatus according to claim 1, further comprising: a stopper memberwhich contacts the half mirror for positioning the half mirror in thefirst state, wherein the stopper member can move with respect to amoving track of the half mirror.
 11. The image taking apparatusaccording to claim 1, wherein the image-taking lens is attachable anddetachable to the image taking apparatus.